Facilitating ambient temperature measurement accuracy in an HVAC controller having internal heat-generating components

ABSTRACT

A smart-home device may include a plurality of temperature sensors, and a processing system that may be configured to operate a first operating state characterized by relatively low power consumption and a corresponding relatively low associated heat generation, and a second operating state characterized by relatively high power consumption and a corresponding relatively high associated heat generation. During time intervals in which the processing system is operating in the first operating state, the processing system may process the temperature sensor measurements according to a first ambient temperature determination algorithm to compute the determined ambient temperature. During time intervals in which the processing system is operating in the second operating state, the processing system may process the temperature sensor measurements according to a second ambient temperature determination algorithm to compute the determined ambient temperature.

CROSS-REFERENCES TO OTHER APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/871,734 filed on Apr. 26, 2013, which is incorporated herein byreference.

TECHNICAL FIELD

This patent specification relates to systems and methods for themonitoring and control of energy-consuming systems or otherresource-consuming systems. More particularly, this patent specificationrelates to control units that govern the operation of energy-consumingsystems, household devices, or other resource-consuming systems,including methods for activating electronic displays for thermostatsthat govern the operation of heating, ventilation, and air conditioning(HVAC) systems.

BACKGROUND OF THE INVENTION

Substantial effort and attention continue toward the development ofnewer and more sustainable energy supplies. The conservation of energyby increased energy efficiency remains crucial to the world's energyfuture. According to an October 2010 report from the U.S. Department ofEnergy, heating and cooling account for 56% of the energy use in atypical U.S. home, making it the largest energy expense for most homes.Along with improvements in the physical plant associated with homeheating and cooling (e.g., improved insulation, higher efficiencyfurnaces), substantial increases in energy efficiency can be achieved bybetter control and regulation of home heating and cooling equipment.

As discussed in the technical publication No. 50-8433, entitled “PowerStealing Thermostats” from Honeywell (1997), early thermostats used abimetallic strip to sense temperature and respond to temperature changesin the room. The movement of the bimetallic strip was used to directlyopen and close an electrical circuit. Power was delivered to anelectromechanical actuator, usually relay or contactor in the HVACequipment whenever the contact was closed to provide heating and/orcooling to the controlled space. Since these thermostats did not requireelectrical power to operate, the wiring connections were very simple.Only one wire connected to the transformer and another wire connected tothe load. Typically, a 24 VAC power supply transformer, the thermostat,and 24 VAC HVAC equipment relay were all connected in a loop with eachdevice having only two required external connections.

When electronics began to be used in thermostats, the fact that thethermostat was not directly wired to both sides of the transformer forits power source created a problem. This meant that the thermostat hadto be hardwired directly from the system transformer. Direct hardwiringa common “C” wire from the transformer to the electronic thermostat maybe very difficult and costly.

Because many households do not have a direct wire from the systemtransformer (such as a “C” wire), some thermostats have been designed toderive power from the transformer through the equipment load. Themethods for powering an electronic thermostat from the transformer witha single direct wire connection to the transformer are called “powerstealing” or “power sharing” methods. The thermostat “steals,” “shares,”or “harvests” its power during the “OFF” periods of the heating orcooling system by allowing a small amount of current to flow through itinto the load coil below the load coil's response threshold (even atmaximum transformer output voltage). During the “ON” periods of theheating or cooling system the thermostat draws power by allowing a smallvoltage drop across itself. Ideally, the voltage drop will not cause theload coil to dropout below its response threshold (even at minimumtransformer output voltage). Examples of thermostats with power stealingcapability include the Honeywell T8600, Honeywell T8400C, and theEmerson Model 1F97-0671. However, these systems do not have powerstorage means and therefore must always rely on power stealing.

Additionally, microprocessor controlled “intelligent” thermostats mayhave more advanced environmental control capabilities that can saveenergy while also keeping occupants comfortable. To do this, thesethermostats require more information from the occupants as well as theenvironments where the thermostats are located. These thermostats mayalso be capable of connection to computer networks, including both localarea networks (or other “private” networks) and wide area networks suchas the Internet (or other “public” networks), in order to obtain currentand forecasted outside weather data, cooperate in so-calleddemand-response programs (e.g., automatic conformance with power alertsthat may be issued by utility companies during periods of extremeweather), enable users to have remote access and/or control thereofthrough their network-connected device (e.g., smartphone, tabletcomputer, PC-based web browser), and other advanced functionalities thatmay require network connectivity.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, a thermostat may be presented. The thermostat mayinclude a housing, a user interface, and one or more temperaturesensors, each of the one or more temperature sensors being configured toprovide temperature sensor measurements, where said one or moretemperature sensors includes a first temperature sensor, a secondtemperature sensor, and a third temperature sensor, each beingpositioned at different locations relative to the housing. Thethermostat may also include a processing system disposed within thehousing, the processing system being configured to be in operativecommunication with the one or more temperature sensors to receive thetemperature sensor measurements, in operative communication with one ormore input devices including said user interface for determining asetpoint temperature, and in still further operative communication witha heating, ventilation, and air conditioning (HVAC) system to controlthe HVAC system based on a comparison of a determined ambienttemperature and the setpoint temperature. In some embodiments, theprocessing system is configured to operate in a plurality of operatingstates including a first operating state characterized by relatively lowpower consumption and a corresponding relatively low associated heatgeneration and a second operating state characterized by relatively highpower consumption and a corresponding relatively high associated heatgeneration. The processing system may be further configured to, duringtime intervals in which the processing system is operating in the firstoperating state, process the temperature sensor measurements accordingto a first ambient temperature determination algorithm based on readingsfrom said first and second temperature sensors to compute the determinedambient temperature. In some embodiments, the first ambient temperaturedetermination algorithm will not use readings from the third temperaturesensor. The processing system may be further configured to, during timeintervals in which the processing system is operating in the secondoperating state, process the temperature sensor measurements accordingto a second ambient temperature determination algorithm based onreadings from said third temperature sensor to compute the determinedambient temperature.

In another embodiment, a method of compensating for internal heating ina thermostat may include determining, using a processing system of thethermostat, a current operating state of the processing system. Thethermostat may include a housing, a user interface, and one or moretemperature sensors, each of the one or more temperature sensors beingconfigured to provide temperature sensor measurements, where the one ormore temperature sensors may include a first temperature sensor, asecond temperature sensor, and a third temperature sensor, each beingpositioned at different locations relative to the housing. Thethermostat may also include a processing system disposed within thehousing, the processing system being configured to be in operativecommunication with the one or more temperature sensors to receive thetemperature sensor measurements, in operative communication with one ormore input devices including said user interface for determining asetpoint temperature, and in still further operative communication witha heating, ventilation, and air conditioning (HVAC) system to controlthe HVAC system based on a comparison of a determined ambienttemperature and the setpoint temperature, where the processing system isconfigured to operate in a plurality of operating states including afirst operating state characterized by relatively low power consumptionand a corresponding relatively low associated heat generation and asecond operating state characterized by relatively high powerconsumption and a corresponding relatively high associated heatgeneration. The method may also include, during time intervals in whichthe processing system is operating in the first operating state,processing the temperature sensor measurements according to a firstambient temperature determination algorithm based on readings from saidfirst and second temperature sensors to compute the determined ambienttemperature. The method may further include, during time intervals inwhich the processing system is operating in the second operating state,processing the temperature sensor measurements according to a secondambient temperature determination algorithm based on readings from saidthird temperature sensor to compute the determined ambient temperature.In some embodiments, the first ambient temperature determinationalgorithm will not use readings from the third temperature sensor.

In yet another embodiment, a thermostat may include one or moretemperature sensors, each of the one or more temperature sensors beingconfigured to provide temperature sensor measurements. The thermostatmay also include a processing system, the processing system beingconfigured to be in operative communication with the one or moretemperature sensors to receive the temperature sensor measurements, andconfigured to be in operative communication with a heating, ventilation,and air conditioning (HVAC) system to control the HVAC system based on acomparison of a determined ambient temperature and a setpointtemperature. The processing system may be configured to operate in aplurality of operating states including a first operating statecharacterized by relatively low power consumption and a correspondingrelatively low associated heat generation and a second operating statecharacterized by relatively high power consumption and a correspondingrelatively high associated heat generation. The processing system mayalso be configured to, during time intervals in which the processingsystem is operating in the first operating state, process thetemperature sensor measurements according to a first ambient temperaturedetermination algorithm to compute the determined ambient temperature.The processing system may further be configured to, during timeintervals in which the processing system is operating in the secondoperating state, process the temperature sensor measurements accordingto a second ambient temperature determination algorithm to compute thedetermined ambient temperature.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings. Also note that other embodiments may bedescribed in the following disclosure and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view of a thermostat, according to oneembodiment.

FIG. 2 illustrates an exploded perspective view of a thermostat having ahead unit and the backplate, according to one embodiment.

FIG. 3A illustrates an exploded perspective view of a head unit withrespect to its primary components, according to one embodiment.

FIG. 3B illustrates an exploded perspective view of a backplate withrespect to its primary components, according to one embodiment.

FIG. 4A illustrates a simplified functional block diagram for a headunit, according to one embodiment.

FIG. 4B illustrates a simplified functional block diagram for abackplate, according to one embodiment.

FIG. 5 illustrates a simplified circuit diagram of a system for managingthe power consumed by a thermostat, according to one embodiment.

FIG. 6 illustrates various views of a thermostat having one or moretemperature sensors, according to some embodiments.

FIG. 7 illustrates a graph of the responses of three temperature sensorswhen the internal components of the thermostat operate in the high powermode, according to some embodiments.

FIG. 8 illustrates a graph of the responses of three temperature sensorswhen the thermostat is heated by internal components operating in ahigh-power mode, according to some embodiments.

FIG. 9 illustrates a graph of actual temperature measurements as thethermostat switches between the first and second ambient temperaturedetermining algorithms, according to some embodiments.

FIG. 10 illustrates a flowchart of an algorithm that may be used toswitch between ambient temperature determination algorithms, accordingto some embodiments.

DETAILED DESCRIPTION OF THE INVENTION

The subject matter of this patent specification relates to the subjectmatter of the following commonly assigned applications, each of which isincorporated by reference herein: U.S. Ser. No. 13/624,881 filed Sep.21, 2012; U.S. Ser. No. 13/624,811 filed Sep. 21, 2012; InternationalApplication No. PCT/US12/00007 filed Jan. 3, 2012; U.S. Ser. No.13/466,815 filed May 8, 2012; U.S. Ser. No. 13/467,025; U.S. Ser. No.13/351,688 filed Jan. 17, 2012, which issued as U.S. Pat. No. 8,195,313on Jun. 5, 2012; and U.S. Ser. No. 13/199,108. The above-referencedpatent applications are collectively referenced herein as “thecommonly-assigned incorporated applications.”

In the following detailed description, for purposes of explanation,numerous specific details are set forth to provide a thoroughunderstanding of the various embodiments of the present invention. Thoseof ordinary skill in the art will realize that these various embodimentsof the present invention are illustrative only and are not intended tobe limiting in any way. Other embodiments of the present invention willreadily suggest themselves to such skilled persons having the benefit ofthis disclosure.

In addition, for clarity purposes, not all of the routine features ofthe embodiments described herein are shown or described. One of ordinaryskill in the art would readily appreciate that in the development of anysuch actual embodiment, numerous embodiment-specific decisions may berequired to achieve specific design objectives. These design objectiveswill vary from one embodiment to another and from one developer toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming but would nevertheless be a routineengineering undertaking for those of ordinary skill in the art havingthe benefit of this disclosure.

It is to be appreciated that while one or more embodiments are describedfurther herein in the context of typical HVAC system used in aresidential home, such as single-family residential home, the scope ofthe present teachings is not so limited. More generally, thermostatsaccording to one or more of the preferred embodiments are applicable fora wide variety of enclosures having one or more HVAC systems including,without limitation, duplexes, townhomes, multi-unit apartment buildings,hotels, retail stores, office buildings, and industrial buildings.Further, it is to be appreciated that while the terms user, customer,installer, homeowner, occupant, guest, tenant, landlord, repair person,and/or the like may be used to refer to the person or persons who areinteracting with the thermostat or other device or user interface in thecontext of one or more scenarios described herein, these references areby no means to be considered as limiting the scope of the presentteachings with respect to the person or persons who are performing suchactions.

Exemplary Thermostat Embodiments

Provided according to one or more embodiments are systems, methods, andcomputer program products for controlling one or more HVAC systems basedon one or more versatile sensing and control units (VSCU units), eachVSCU unit being configured and adapted to provide sophisticated,customized, energy-saving HVAC control functionality while at the sametime being visually appealing, non-intimidating, and easy to use. Theterm “thermostat” is used herein below to represent a particular type ofVSCU unit (Versatile Sensing and Control) that is particularlyapplicable for HVAC control in an enclosure. Although “thermostat” and“VSCU unit” may be seen as generally interchangeable for the contexts ofHVAC control of an enclosure, it is within the scope of the presentteachings for each of the embodiments herein to be applied to VSCU unitshaving control functionality over measurable characteristics other thantemperature (e.g., pressure, flow rate, height, position, velocity,acceleration, capacity, power, loudness, brightness) for any of avariety of different control systems involving the governance of one ormore measurable characteristics of one or more physical systems, and/orthe governance of other energy or resource consuming systems such aswater usage systems, air usage systems, systems involving the usage ofother natural resources, and systems involving the usage of variousother forms of energy.

FIGS. 1-5 and the descriptions in relation thereto provide exemplaryembodiments of thermostat hardware and/or software that can be used toimplement the specific embodiments of the appended claims. Thisthermostat hardware and/or software is not meant to be limiting, and ispresented to provide an enabling disclosure. FIG. 1 illustrates aperspective view of a thermostat 100, according to one embodiment. Inthis specific embodiment, the thermostat 100 can be controlled by atleast two types of user input, the first being a rotation of the outerring 112, and the second being an inward push on an outer cap 108 untilan audible and/or tactile “click” occurs. As used herein, these twotypes of user inputs, may be referred to as “manipulating” thethermostat. In other embodiments, manipulating the thermostat may alsoinclude pressing keys on a keypad, voice recognition commands, and/orany other type of input that can be used to change or adjust settings onthe thermostat 100.

For this embodiment, the outer cap 108 can comprise an assembly thatincludes the outer ring 112, a cover 114, an electronic display 116, anda metallic portion 124. Each of these elements, or the combination ofthese elements, may be referred to as a “housing” for the thermostat100. Simultaneously, each of these elements, or the combination of theseelements, may also form a user interface. The user interface mayspecifically include the electronic display 116. In FIG. 1, the userinterface 116 may be said to operate in an active display mode. Theactive display mode may include providing a backlight for the electronicdisplay 116. In other embodiments, the active display mode may increasethe intensity and/or light output of the electronic display 116 suchthat a user can easily see displayed settings of the thermostat 100,such as a current temperature, a setpoint temperature, an HVAC function,and/or the like. The active display mode may be contrasted with aninactive display mode (not shown). The inactive display mode can disablea backlight, reduce the amount of information displayed, lessen theintensity of the display, and/or altogether turn off the electronicdisplay 116, depending on the embodiment.

Depending on the settings of the thermostat 100, the active display modeand the inactive display mode of the electronic display 116 may also orinstead be characterized by the relative power usage of each mode. Inone embodiment, the active display mode may generally requiresubstantially more electrical power than the inactive display mode. Insome embodiments, different operating modes of the electronic display116 may instead be characterized completely by their power usage. Inthese embodiments, the different operating modes of the electronicdisplay 116 may be referred to as a first mode and a second mode, wherethe user interface requires more power when operating in the first modethan when operating in the second mode.

According to some embodiments the electronic display 116 may comprise adot-matrix layout (individually addressable) such that arbitrary shapescan be generated, rather than being a segmented layout. According tosome embodiments, a combination of dot-matrix layout and segmentedlayout is employed. According to some embodiments, electronic display116 may be a backlit color liquid crystal display (LCD). An example ofinformation displayed on the electronic display 116 is illustrated inFIG. 1, and includes central numerals 120 that are representative of acurrent setpoint temperature. According to some embodiments, metallicportion 124 can have a number of slot-like openings so as to facilitatethe use of a sensors 130, such as a passive infrared motion sensor(PIR), mounted beneath the slot-like openings.

According to some embodiments, the thermostat 100 can include additionalcomponents, such as a processing system 160, display driver 164, and awireless communications system 166. The processing system 160 canadapted or configured to cause the display driver 164 to cause theelectronic display 116 to display information to the user. Theprocessing system 160 can also be configured to receive user input viathe rotatable ring 112. These additional components, including theprocessing system 160, can be enclosed within the housing, as displayedin FIG. 1. These additional components are described in further detailherein below.

The processing system 160, according to some embodiments, is capable ofcarrying out the governance of the thermostat's operation. For example,processing system 160 can be further programmed and/or configured tomaintain and update a thermodynamic model for the enclosure in which theHVAC system is installed. According to some embodiments, the wirelesscommunications system 166 can be used to communicate with devices suchas personal computers, remote servers, handheld devices, smart phones,and/or other thermostats or HVAC system components. These communicationscan be peer-to-peer communications, communications through one or moreservers located on a private network, or and/or communications through acloud-based service.

Motion sensing as well as other techniques can be use used in thedetection and/or prediction of occupancy. According to some embodiments,occupancy information can be a used in generating an effective andefficient scheduled program. For example, an active proximity sensor170A can be provided to detect an approaching user by infrared lightreflection, and an ambient light sensor 170B can be provided to sensevisible light. The proximity sensor 170A can be used in conjunction witha plurality of other sensors to detect proximity in the range of aboutone meter so that the thermostat 100 can initiate “waking up” when theuser is approaching the thermostat and prior to the user touching thethermostat. Such use of proximity sensing is useful for enhancing theuser experience by being “ready” for interaction as soon as, or verysoon after the user is ready to interact with the thermostat. Further,the wake-up-on-proximity functionality also allows for energy savingswithin the thermostat by “sleeping” when no user interaction is takingplace or about to take place. The various types of sensors that may beused, as well as the operation of the “wake up” function are describedin much greater detail throughout the remainder of this disclosure.

In some embodiments, the thermostat can be physically and/orfunctionally divided into at least two different units. Throughout thisdisclosure, these two units can be referred to as a head unit and abackplate. FIG. 2 illustrates an exploded perspective view 200 of athermostat 208 having a head unit 210 and a backplate 212, according toone embodiment. Physically, this arrangement may be advantageous duringan installation process. In this embodiment, the backplate 212 can firstbe attached to a wall, and the HVAC wires can be attached to a pluralityof HVAC connectors on the backplate 212. Next, the head unit 210 can beconnected to the backplate 212 in order to complete the installation ofthe thermostat 208.

FIG. 3A illustrates an exploded perspective view 300 a of a head unit330 with respect to its primary components, according to one embodiment.Here, the head unit 330 may include an electronic display 360. Accordingto this embodiment, the electronic display 360 may comprise an LCDmodule. Furthermore, the head unit 330 may include a mounting assembly350 used to secure the primary components in a completely assembled headunit 330. The head unit 330 may further include a circuit board 340 thatcan be used to integrate various electronic components described furtherbelow. In this particular embodiment, the circuit board 340 of the headunit 330 can include a manipulation sensor 342 to detect usermanipulations of the thermostat. In embodiments using a rotatable ring,the manipulation sensor 342 may comprise an optical finger navigationmodule as illustrated in FIG. 3A. A rechargeable battery 344 may also beincluded in the assembly of the head unit 330. In one preferredembodiment, rechargeable battery 344 can be a Lithium-Ion battery, whichmay have a nominal voltage of 3.7 volts and a nominal capacity of 560mAh.

FIG. 3B illustrates an exploded perspective view 300 b of a backplate332 with respect to its primary components, according to one embodiment.The backplate 332 may include a frame 310 that can be used to mount,protect, or house a backplate circuit board 320. The backplate circuitboard 320 may be used to mount electronic components, including one ormore processing functions, and/or one or more HVAC wire connectors 322.The one or more HVAC wire connectors 322 may include integrated wireinsertion sensing circuitry configured to determine whether or not awire is mechanically and/or electrically connected to each of the one ormore HVAC wire connectors 322. In this particular embodiment, tworelatively large capacitors 324 are a part of power stealing circuitrythat can be mounted to the backplate circuit board 320. The powerstealing circuitry is discussed further herein below.

In addition to physical divisions within the thermostat that simplifyinstallation process, the thermostat may also be divided functionallybetween the head unit and the backplate. FIG. 4A illustrates asimplified functional block diagram 400 a for a head unit, according toone embodiment. The functions embodied by block diagram 400 a arelargely self-explanatory, and may be implemented using one or moreprocessing functions. As used herein, the term “processing function” mayrefer to any combination of hardware and/or software. For example, aprocessing function may include a microprocessor, a microcontroller,distributed processors, a lookup table, digital logic,logical/arithmetic functions implemented in analog circuitry, and/or thelike. A processing function may also be referred to as a processingsystem, a processing circuit, or simply a circuit.

In this embodiment, a processing function on the head unit may beimplemented by an ARM processor. The head unit processing function mayinterface with the electronic display 402, an audio system 404, and amanipulation sensor 406 as a part of a user interface 408. The head unitprocessing function may also facilitate wireless communications 410 byinterfacing with various wireless modules, such as a Wi-Fi module 412and/or a ZigBee module 414. Furthermore, the head unit processingfunction may be configured to control the core thermostat operations416, such as operating the HVAC system. The head unit processingfunction may further be configured to determine or sense occupancy 418of a physical location, and to determine building characteristics 420that can be used to determine time-to-temperature characteristics. Usingthe occupancy sensing 418, the processing function on the head unit mayalso be configured to learn and manage operational schedules 422, suchas diurnal heat and cooling schedules. A power management module 462 maybe used to interface with a corresponding power management module on theback plate, the rechargeable battery, and a power control circuit 464 onthe back plate.

Additionally, the head unit processing function may include and/or becommunicatively coupled to one or more memories. The one or morememories may include one or more sets of instructions that cause theprocessing function to operate as described above. The one or morememories may also include a sensor history and global state objects 424.The one or more memories may be integrated with the processing function,such as a flash memory or RAM memory available on many commercialmicroprocessors. The head unit processing function may also beconfigured to interface with a cloud management system 426, and may alsooperate to conserve energy wherever appropriate 428. An interface 432 toa backplate processing function 430 may also be included, and may beimplemented using a hardware connector.

FIG. 4B illustrates a simplified functional block diagram for abackplate, according to one embodiment. Using an interface 436 that ismatched to the interface 432 shown in FIG. 4A, the backplate processingfunction can communicate with the head unit processing function 438. Thebackplate processing function can include wire insertion sensing 440that is coupled to external circuitry 442 configured to provide signalsbased on different wire connection states. The backplate processingfunction may be configured to manage the HVAC switch actuation 444 bydriving power FET circuitry 446 to control the HVAC system.

The backplate processing function may also include a sensor pollinginterface 448 to interface with a plurality of sensors. In thisparticular embodiment, the plurality of sensors may include atemperature sensor, a humidity sensor, a PIR sensor, a proximity sensor,an ambient light sensor, and or other sensors not specifically listed.This list is not meant to be exhaustive. Other types of sensors may beused depending on the particular embodiment and application, such assound sensors, flame sensors, smoke detectors, and/or the like. Thesensor polling interface 448 may be communicatively coupled to a sensorreading memory 450. The sensor reading memory 450 can store sensorreadings and may be located internally or externally to amicrocontroller or microprocessor.

Finally, the backplate processing function can include a powermanagement unit 460 that is used to control various digital and/oranalog components integrated with the backplate and used to manage thepower system of the thermostat. Although one having skill in the artwill recognize many different implementations of a power managementsystem, the power management system of this particular embodiment caninclude a bootstrap regulator 462, a power stealing circuit 464, a buckconverter 466, and/or a battery controller 468.

FIG. 5 illustrates a simplified circuit diagram 500 of a system formanaging the power consumed by a thermostat, according to oneembodiment. The powering circuitry 510 comprises a full-wave bridgerectifier 520, a storage and waveform-smoothing bridge output capacitor522 (which can be, for example, on the order of 30 microfarads), a buckregulator circuit 524, a power-and-battery (PAB) regulation circuit 528,and a rechargeable lithium-ion battery 530. In conjunction with othercontrol circuitry including backplate power management circuitry 527,head unit power management circuitry 529, and the microcontroller 508,the powering circuitry 510 can be configured and adapted to have thecharacteristics and functionality described herein below.

By virtue of the configuration illustrated in FIG. 5, when there is a“C” wire presented upon installation, the powering circuitry 510operates as a relatively high-powered, rechargeable-battery-assistedAC-to-DC converting power supply. When there is not a “C” wirepresented, the powering circuitry 510 operates as a power-stealing,rechargeable-battery-assisted AC-to-DC converting power supply. Thepowering circuitry 510 generally serves to provide the voltage Vcc MAINthat is used by the various electrical components of the thermostat,which in one embodiment can be about 4.0 volts. For the case in whichthe “C” wire is present, there is no need to worry about accidentallytripping (as there is in inactive power stealing) or untripping (foractive power stealing) an HVAC call relay, and therefore relativelylarge amounts of power can be assumed to be available. Generally, thepower supplied by the “C” wire will be greater than the instantaneouspower required at any time by the remaining circuits in the thermostat.

However, a “C” wire will typically only be present in about 20% ofhomes. Therefore, the powering circuitry 510 may also be configured to“steal” power from one of the other HVAC wires in the absence of a “C”wire. As used herein, “inactive power stealing” refers to the powerstealing that is performed during periods in which there is no activecall in place based on the lead from which power is being stolen. Thus,for cases where it is the “Y” lead from which power is stolen, “inactivepower stealing” refers to the power stealing that is performed whenthere is no active cooling call in place. As used herein, “active powerstealing” refers to the power stealing that is performed during periodsin which there is an active call in place based on the lead from whichpower is being stolen. Thus, for cases where it is the “Y” lead fromwhich power is stolen, “active power stealing” refers to the powerstealing that is performed when there is an active cooling call inplace. During inactive or active power stealing, power can be stolenfrom a selected one of the available call relay wires. While a completedescription of the power stealing circuitry 510 can be found in thecommonly assigned applications that have been previously incorporatedherein by reference, the following brief explanation is sufficient forpurposes of this disclosure.

Some components in the thermostat, such as the head unit processingfunction, the user interface, and/or the electronic display may consumemore instantaneous power than can be provided by power stealing alone.When these more power-hungry components are actively operating, thepower supplied by power stealing can be supplemented with therechargeable battery 530. In other words, when the thermostat is engagedin operations, such as when the electronic display is in an activedisplay mode, power may be supplied by both power stealing and therechargeable battery 530. In order to preserve the power stored in therechargeable battery 530, and to give the rechargeable battery 530 anopportunity to recharge, some embodiments optimize the amount of timethat the head unit processing function and the electronic display areoperating in an active mode. In other words, it may be advantageous insome embodiments to keep the head unit processing function in a sleepmode or low power mode and to keep the electronic display in an inactivedisplay mode as long as possible without affecting the user experience.

When the head unit processing function and the electronic display are inan inactive or sleep mode, the power consumed by the thermostat isgenerally less than the power provided by power stealing. Therefore, thepower that is not consumed by the thermostat can be used to recharge therechargeable battery 530. In this embodiment, the backplate processingfunction 508 (MSP430) can be configured to monitor the environmentalsensors in a low-power mode, and then wake the head unit processingfunction 532 (AM3703) when needed to control the HVAC system, etc.Similarly, the backplate processing function 508 can be used to monitorsensors used to detect the closeness of a user, and wake the head unitprocessing system 532 and/or the electronic display when it isdetermined that a user intends to interface with the thermostat.

It will be understood by one having skill in the art that the variousthermostat embodiments depicted and described in relation to FIGS. 1-5are merely exemplary and not meant to be limiting. Many other hardwareand/or software configurations may be used to implement a thermostat andthe various functions described herein below, including those describedin described in U.S. Ser. No. 13/624,881, supra, and U.S. Ser. No.13/624,811, supra. These embodiments should be seen as an exemplaryplatform in which the following embodiments can be implemented toprovide an enabling disclosure. Of course, the following methods,systems, and/or software program products could also be implementedusing different types of thermostats, different hardware, and/ordifferent software.

Self-Heating Correction Configurations

One issue that can arise in relation to the thermostatic control of anHVAC system for many homes and businesses (hereinafter “enclosures”)relates to scenarios in which temperature sensors used to calculate adetermined ambient temperature may be heated by internal electroniccomponents of the thermostat to a point where an algorithm fordetermining the ambient temperature during low-power operation is nolonger accurate.

Modern smart thermostats may include electronic components such asmicroprocessors and electronic displays that may generate heat duringuse. Oftentimes, one or more temperature sensors used by the thermostatmay be located in close proximity to the internal heat-generatingcomponents. Furthermore, a thermostat housing, along with othermechanical thermostat components, may create an insulating effect oninternal temperature sensors. These factors may combine to distort rawtemperature sensor measurements such that these raw temperature sensormeasurements do not represent an accurate representation of the ambienttemperature within an enclosure.

When subject to the internal heating described above, it can oftenhappen that the internals of the thermostat body heat up, along withpossibly the ambient temperature in the vicinity of the thermostat. Thismay cause the thermostat to perceive a sensed ambient temperature forthe air in the enclosure that is significantly lower than the actualambient air temperature in the enclosure according to equations to bediscussed below. Because the thermostat “thinks” that the enclosuretemperature is lower than it really is, the thermostat controls the HVACsystem to make or allow the enclosure to become hotter than it wouldotherwise become. This can cause occupant discomfort in the summertimedue to insufficient cooling, and furthermore can cause both occupantdiscomfort and wasted energy in the wintertime due to excessive heating.Even an artificial temperature increase of a few degrees may besufficient to activate an HVAC heating system every time a userinteracts with the thermostat and turns on the user interface.

Many modern smart thermostats use an ambient temperature determinationalgorithm that compensates for heat generated by internal electroniccomponents of the thermostat. Generally, these algorithms estimate anambient temperature that is lower than the measured temperature of oneor more internal temperature sensors. These ambient temperaturedetermination algorithms are configured to compensate for anear-constant level of internal heating. For example, a thermostat mayinclude a low-power processor and a basic electronic display that arealways active, and therefore generate a near-constant level of heat thatis absorbed by the thermostat.

However, some modern smart thermostats, such as the exemplary embodimentdescribed in the preceding section, may include high-power processors,state-switching transistors, and/or advanced electronic displays. Asdescribed above, these higher power electronics may be operated in aplurality of different operating states. The first operating state maybe associated with a relatively low level of power consumption, alongwith a corresponding relatively low level of internal heat generation. Asecond operating state may be associated with a relatively high level ofpower consumption, along with a corresponding relatively high level ofinternal heat generation.

A thermostat may compensate to some degree for internal heating bydetermining an ambient temperature based on temperature measurementsprovided by a first temperature sensor and a second temperature sensor.Typically, the second temperature sensor may be located closer to theheat-generating components than the first temperature sensor, such as onthe head unit circuit board. The first temperature sensor may be locatedfurther away from the heat-generating components, such as on an insidesurface of the housing of the thermostat. However, it has beendiscovered that when the internal electronics operate in the relativelyhigh power state, the second temperature sensor will heat up faster thanthe first temperature sensor, causing the determined ambient temperatureto artificially drop according to equations discussed in further detailbelow.

Embodiments described herein may solve this problem by including a thirdtemperature sensor. In some embodiments, the third temperature sensormay be located such that it is not as susceptible to internal heating aseither the first or second temperature sensors. For example, the thirdtemperature sensor may be located towards the bottom of the backplate ofthe exemplary thermostat described above. Because of its location, thebackplate temperature sensor may be less susceptible to internal heatingand generally tracks the ambient enclosure temperature according to anarithmetic offset.

In some embodiments, the thermostat may generally detect time intervalswhere excess self-heating may occur, and in response the thermostat canswitch between temperature sensors and/or equations that are used tocalculate the determined ambient temperature. During intervals whenexcessive internal heating is not detected, the determined ambienttemperature can be calculated as a function of the head unit (second)temperature sensor and the housing (first) temperature sensor. Duringintervals when excess internal heating is detected, the determinedambient temperature can be calculated as a function of the backplate(third) temperature sensor and an offset calculated by historical data.

In order to reduce false positives and false negatives, a state machinemay first detect time intervals where the thermostat components areoperating in a relatively high-power state. At this point, the statemachine may then begin watching for a temperature divergence, i.e. adrop in the determined ambient temperature that diverges from thetemperature measurements provided by the third temperature sensor bymore than a threshold amount over a predetermined time period. When atemperature divergence coincides with the thermostat componentsoperating in the relatively high-power state, the thermostat may switchbetween ambient temperature determination algorithms.

In some embodiments, internal heating compensation methods may becombined with external heating compensation methods that compensate forexposure to direct sunlight. The state machines for these two methodsmay be combined in order to provide a single set of wake-up conditionsfor the backplate processor.

The concepts described in this patent application may be broadly appliedto any circumstance where intermittent environmental anomalies oroperational states give reason to distrust techniques used to monitorenvironmental sensors during normal operation. Specifically, the idea ofusing secondary sensor readings combined with known system operatingmodes may be used to determine when a primary sensor is no longerreliable. When the unreliability of a primary sensor is detected,thresholds can be adjusted or alternate algorithms can be employed tocompensate for the environmental anomalies causing the distortedreadings by the primary sensor.

In addition to heating generated by internal electronics, the thermostatmay also be heated by external stimuli. In one case, the user mayinteract with a thermostat for extended time interval. For example,during an initial set up or during menu operations, a user may use theirhand to interact with the user interface of the thermostat, such as arotatable ring. These types of user interfaces may necessitatenear-constant user contact with thermostat housing. Therefore, heat fromthe user's hand may be transferred to the thermostat, and may in turnirregularly heat one or more of the temperature sensors. The algorithmsdescribed herein may also be altered to detect interactions with theuser interface that would be sufficient to cause irregular temperaturemeasurements, particularly in the first temperature sensor as describedbelow.

Other applications might include a smoke detector that senses watervapor when dinner is being cooked, when someone is in the shower, orwhen other environmental conditions occur where the smoke sensor maydetect a false positive. Home security systems could adjust monitoringconditions or sensor thresholds automatically when users interact withthe system. Temperature sensors in a refrigerator could be calibrated tocompensate for instances when separation switches detect users openingthe refrigerator door. Additionally, many home electronic systems, suchas TVs, stereos, receivers, and video players, may generate significantinternal heat during certain types of operations. This excess heat maynot only affect temperature sensors, but also other sensors that aresensitive to rapid temperature increases. By determining when high-poweroperating states occur, determinations based on internal sensor readingsmay be altered accordingly. On a broader scale, a central monitoringstation can detect environmental anomalies, such as earthquakes, forestfires, and other atmospheric disturbances that may cause environmentalmonitoring systems inside of a home to malfunction. For example, nearbyforest fires may set off home smoke detectors when a home's windows areopen. The central monitoring station could transmit this information toeach home sensing device and adjust thresholds or algorithmsaccordingly. Conversely, wide-scale sensor responses could betransmitted to a central monitoring station to detect environmentalanomalies. For example, many smoke detectors going off in the same areamay indicate a nearby forest fire.

FIG. 6 illustrates various views of a thermostat having one or moretemperature sensors, according to some embodiments. Note that theembodiment of FIG. 6 is merely exemplary. Other embodiments may includemore or fewer temperature sensors, and the temperature sensors may bedisposed in different locations and/or orientations within the housingof the thermostat. For some embodiments, one or more of the featuresdescribed herein are advantageously applied to one or more of thespatially compact, visually pleasing thermostat devices described inU.S. Ser. No. 13/624,881, supra, and U.S. Ser. No. 13/624,811, supra.Referring now again to FIG. 6, for this particular embodiment there isincluded three distinct temperature sensors. A first temperature sensor610 may be disposed near a housing 608 of the thermostat 602. In oneembodiment, the first temperature sensor 610 may be affixed to aninternal portion of the housing 608. In some embodiments, the firsttemperature sensor 610 may be disposed within the housing 608 such thatit is near a front portion of the thermostat 602, near a user interfaceof the thermostat 602, and/or relatively farther away from internal heatsources of the thermostat 602, such as a processing system,microprocessors, high-power sensors, power transistors, and/or the like.

The positioning of the first temperature sensor 610 may be describedrelative to a second temperature sensor 612. In some embodiments, thesecond temperature sensor 612 may be disposed on a circuit boardinternal to the thermostat 602. In the exemplary thermostat describedabove, a circuit board 606 in a head unit may be a suitable location tomount the second temperature sensor 612. The second temperature sensor612 may also be referred to as a head unit temperature sensor. The firsttemperature sensor 610 may be disposed closer to the housing 608 of thethermostat 602 than the second temperature sensor 612. The secondtemperature sensor 612 may be disposed closer to the internalelectronics of the thermostat 602 than the first temperature sensor 610.

The first temperature sensor 610 and the second temperature sensor 612may also be characterized by how they are affected by internaltemperature changes. The first temperature sensor 610 may respond morequickly to ambient temperature changes in the enclosure than the secondtemperature sensor 612. The second temperature sensor 612 may respondmore quickly to heating caused by internal electronic components of thethermostat 602 than the first temperature sensor 610. In some cases, thefirst temperature sensor 610 may be described as being more linked tothe external housing and the environment of the enclosure, while thesecond temperature sensor 612 may be described as being less linked tothe external housing, but more linked to the internal heat-generatingcomponents of the thermostat.

Generally, the thermostat 602 does not simply accept raw temperaturemeasurements provided by the one or more temperature sensors as anaccurate representation of the ambient temperature in the enclosure. Insome cases, the one or more temperature sensors may be disposed withinthe housing 608 of the thermostat 602, and may therefore be somewhatthermally insulated from the ambient temperature in the enclosure asdescribed above. The one or more temperature sensors may also beaffected by heat generated by internal electronic components of thethermostat 602. Microprocessors, microcontrollers, power sources, powerregulating circuitry, power stealing circuitry, wireless communicationscircuitry, and user interface circuitry may all generate varying amountsof heat during operation of the thermostat 602. Because each of the oneor more thermostats may be disposed at varying distances from theheat-generating components, the raw temperature sensor measurements maygenerally be higher than the actual ambient temperature of theenclosure.

Therefore, instead of using temperature sensor measurements provided bythe one or more temperature sensors, the thermostat 602 may insteadcalculate a determined ambient temperature. As used herein, the term“determined ambient temperature” may refer to a temperature thatdetermined by a processing system of the thermostat 602 as a function ofthe raw temperature sensor measurements provided by the one or moretemperature sensors. Merely by way of example, the determined ambienttemperature may be calculated by comparing the measurements from thefirst temperature sensor 610 to the measurements from the secondtemperature sensor 612, or by adding an offset to measurements from oneof the one or more temperature sensors.

During time intervals in which it is determined that the thermostat 602is operating in a relatively low power state, a first ambienttemperature determination algorithm may be used to compute thedetermined ambient temperature. This first ambient temperaturedetermination algorithm may leverage the fact that the first temperaturesensor 610 and the second temperature sensor 612 may be affecteddifferently by the heat-generating components of the thermostat 602. Inone embodiment, the first ambient temperature determination algorithmmay calculate the determined ambient temperature using the followingequation.T _(det) =T ₁ −k(T ₂ −T ₁)  (1)

In equation (1), T_(det) represents the determined ambient temperature,T₁ represents the temperature sensor measurements provided by the firsttemperature sensor 610, T₂ represents the temperature sensormeasurements provided by the second temperature sensor 612, and krepresents a constant that may depend on the characteristics of thethermostat 602 and/or the enclosure. In one embodiment, the value of kmay be approximately 1.0.

The equation and method described above may be used to calculate thedetermined ambient temperature using at least two temperature sensors.Other embodiments may alter equation (1) to include additionaltemperature sensors. Generally, equation (1) may provide an accurateestimation of the ambient temperature of the enclosure during normaloperation. However, situations have been discovered where this firstambient temperature determination algorithm is not adequate. One suchsituation involves times when the thermostat is operating in arelatively high-power state.

As used herein, the “relatively high-power state,” or simply “high-powerstate,” may characterize times when a main processor of the thermostatprocessing system operates in a wake state as opposed to in a sleepstate. The relatively high-power state may also characterize times whena user interface is active as opposed to times when the user interfaceis inactive. The relatively high-power state may also characterize timeswhen excessive heat may be generated using power stealing circuitry,power switching transistors, battery charging circuitry, and/or thelike. The relatively high-power state may occur in response to a singleelectronic component generating excessive heat, or may occur in responseto a combination of electronic components generating excessive heat. Forexample, the thermostat may operate in the high-power state when a userinteracts with the user interface, and/or when a main processortransitions to an awake state to perform periodic calculations.

The heat generated by the internal electronics may be readilytransferred to the second temperature sensor 612 by heating the circuitboard 606 or by heating the internal environment of the thermostat 602.When the thermostat operates in the high-power state, the secondtemperature sensor 612 may be heated much faster than the firsttemperature sensor 610. This may cause the determined ambienttemperature calculated by equation (1) to be lower than the actualambient temperature. Because equation (1) is configured to calculate adetermined ambient temperature based on a constant level of internalheating, these periodic spikes of excessive internal heating can corruptthese calculations.

When exposed to excessive internal heating, the second temperaturesensor 612 tends to heat before the excessive internal heating begins toaffect the first temperature sensor 610. Additionally, the secondtemperature sensor 612 will tend to heat at a faster rate than the firsttemperature sensor 610. In other words, the slope of the temperaturemeasurements provided over time by the second temperature sensor 612will be steeper than the temperature measurements provided over time bythe first temperature sensor 610 when the thermostat is operating in thehigh-power state. According to equation (1) the determined ambienttemperature is a function of the difference between the firsttemperature sensor 610 and the second temperature sensor 612. As thisdifference is artificially increased by excessive internal heating, thedetermined ambient temperature may drop at an even faster rate than thatof the second temperature sensor 612.

To overcome the problem of excessive internal heating, some embodimentsdescribed herein may incorporate a third temperature sensor 614 into thedesign of the thermostat 602. The third temperature sensor 614 may beadded to a portion of the thermostat 602 that is somewhat thermallyisolated from the influence of internal heating compared to the othersensors. In this particular embodiment, the third temperature sensor 614may be added to the backplate 604 of the thermostat 602. The thirdtemperature sensor 614 may be disposed towards the bottom of thebackplate 604, as it has been determined that internally generated heatrises away from the bottom of the thermostat 602. In some embodiments,insulating materials may also be incorporated into or around the thirdtemperature sensor 614 in order to make the third temperature sensor 614respond the slowest to internal heating effects out of the threetemperature sensors.

Although the terms backplate and head unit are used to refer todifferent sections of the exemplary thermostat 602, this description maybe generalized to cover any thermostat that comprises two modularsections. For example, a first modular section may include the thirdtemperature sensor 614 and may be physically secured to a mountingsurface within the enclosure while remaining physically separate from asecond modular section of the thermostat 602. The second modular sectionmay include the first temperature sensor 610 and the second temperaturesensor 612, and may be secured to the first modular section after thefirst modular section has been secured to the mounting surface. In someembodiments, the backplate 604 may form the first modular section, whilethe head unit may form the second modular section.

In some embodiments, the third temperature sensor 614 may be lesssensitive than the second temperature sensor 612 and/or the firsttemperature sensor 610. In one embodiment, the third temperature sensor614 may be combined with a humidity sensor in the same integratedcircuit. The reduced sensitivity of the third temperature sensor 614 maybe advantageous in that it prevents the third temperature sensor 614from responding immediately to the effects of excessive internalheating. The third temperature sensor 614 may also be used as a backupsensor in the case of a malfunctioning first temperature sensor 610and/or second temperature sensor 612. The third temperature sensor 614may also be used in cases where the head unit 606 is separated from thebackplate 604. In some embodiments, the third temperature sensor 614 mayalso be used to monitor heat generated by the internal electronics ofthe backplate 604.

Many different types of commercially available sensors may be used toimplement the various temperature sensors used by the thermostat 602.Merely by way of example, the first temperature sensor 610 and/or thesecond temperature sensor 612 may be implemented using the TMP112high-precision, low-power, digital temperature sensor available fromTexas Instruments®. The third temperature sensor 614 may be implementedusing the SHT20 digital humidity sensor chip available from Sensirion®.

FIG. 7 illustrates a graph 700 of the responses of three temperaturesensors when the internal components of the thermostat begin to operatein the high power mode, according to some embodiments. The temperaturemeasurements provided on graph 700 may correspond to the threetemperature sensors described above. Specifically, curve 714 mayrepresent temperature measurements provided over time by the thirdtemperature sensor 614, curve 712 may represent temperature measurementsprovided over time by the second temperature sensor 612, and curve 710may represent temperature measurements provided over time by the firsttemperature sensor 610. Curve 716 may represent the determined ambienttemperature as calculated by the first temperature determinationalgorithm. For example, curve 716 may be generated using equation (1) asa function of T₁ and T₂.

Prior to time t₁, the determined ambient temperature curve 716 may beless than any of the temperature sensor measurements provided by any ofthe one or more temperature sensors. Generally, the more isolated theparticular temperature sensor is from the ambient temperature of theenclosure, the warmer the steady-state measured temperature of theparticular temperature sensor will be. Therefore, the third temperaturesensor curve 714 will generally be higher than the second temperaturesensor curve 712, which in turn will generally be higher than the firsttemperature sensor curve 710 during steady-state conditions.

At time t₁, it may be assumed that the temperature sensors of thethermostat begin to respond to heat generated by thermostat componentsoperating in a high power state. Generally, the temperature sensors maybegin to respond at times and at rates that are related to their thermalisolation from the heating effects of the internal components. Forexample, the second temperature sensor curve 712 may begin to rise firstand at the fastest rate. Next, the first temperature sensor curve 710may begin to rise at a time later than that of the second temperaturesensor curve 712 and at a slower rate than that of the secondtemperature sensor curve 712. Similarly, the third temperature sensorcurve 714 may begin to rise a later time than that of the firsttemperature sensor curve 710 and at a slower rate than that of the firsttemperature sensor curve 710.

The effects upon the determined ambient temperature curve 716 that iscomputed by the first ambient temperature determination algorithm mayalso be significant. As the difference between the first temperaturesensor curve 710 and the second temperature sensor curve 712 increases,the slope of the determined ambient temperature curve 716 may decreaseat an even more dramatic rate. As illustrated by FIG. 7, because of thevarying effects upon the temperature sensors of the thermostat, thefirst ambient temperature determination algorithm may calculate adetermined ambient temperature that begins to dip below the actualambient temperature of the enclosure.

In some cases, actual data has shown that internal heating effects cancorrupt the temperature calculations by as much as 1 to 5 degrees. Thismiscalculation has the potential to dramatically affect the HVAC systemoperation in financially important ways. For example, during the winter,temperature miscalculations may cause an increase in the usage of ahome's heater. Heating in cold climates represents one of the mostcostly monthly bills for homeowners. In the summertime, the consequencesmay be comparably severe. Heating by internal components operating inthe high-power state may cause the temperature in the house to increaseevery time a user interacts with the thermostat. Time-to-temperaturealgorithms operating within an advanced thermostat may determine thatthe difference between the actual temperature and the setpointtemperature is great enough that both primary and secondary HVAC systemsmay need to be activated. This may cause dangerous or costly conditionsfor a home owner.

At a time near time t₁, the thermostat may determine that one or morecomponents are operating in a high-power mode. In response, thethermostat may switch between ambient temperature determinationalgorithms. In some embodiments, a second ambient temperaturedetermination algorithm may be used during time intervals when thethermostat determines that internal components are heating thethermostat and causing the determined ambient temperature calculated bythe first ambient temperature determination algorithm to becomeunreliable.

As may also be observed in FIG. 7, the third temperature sensor curve714 is not rapidly affected by the internal heat generated by componentsoperating in the high-power mode. As described above, the thirdtemperature sensor 614 may be disposed within the thermostat such thatit is more thermally isolated from the effects of component-relatedheating than the other temperature sensors. In one embodiment, thestability exhibited by the third temperature sensor 614 may be used bythe second ambient temperature determination algorithm to calculate thedetermined ambient temperature.

FIG. 8 illustrates a graph 800 of the responses of three temperaturesensors when the thermostat is heated by internal components operatingin a high-power mode, according to some embodiments. Curve 814 mayrepresent temperature measurements provided over time by the thirdtemperature sensor 614, curve 812 may represent temperature measurementsprovided over time by the second temperature sensor 612, and curve 810may represent temperature measurements provided over time by the firsttemperature sensor 610. Curve 816 may represent the determined ambienttemperature as calculated by the second temperature determinationalgorithm.

In some embodiments, a relationship between the third temperature sensorcurve 814 and the determined ambient temperature curve 816 may beobserved during time intervals where internal components are notoperating in the high-power mode and thus not heating the thermostat.During these intervals, the determined ambient temperature may becalculated using the first ambient temperature determination algorithmthat need not depend on the third temperature sensor. For example, anoffset temperature 820 may be measured during these intervals and storedby the thermostat. Using historical data, the offset temperature 820 maybe calculated using the following equation.T _(offset) =T ₃ −T _(det)  (2)

During normal operations, it has been observed that the actualtemperature may track the temperature measured by the third temperaturesensor. In one embodiment, the offset temperature 820 may be calculatedusing historical values for the determined ambient temperature andmeasurements provided by the third temperature sensor over a timeinterval of approximately 30 minutes prior to detecting internalcomponents operating in the high-power mode. Other embodiments may useother time interval lengths, such as approximately 10 minutes, 25minutes, 35 minutes, and 1 hour. At a time near time t₁, the thermostatmay determine that internal components are operating in the high-powermode and switch to the second ambient temperature determinationalgorithm. In one embodiment where the offset temperature 820 has beendetermined, the second ambient temperature determination algorithm maycalculate the determined ambient temperature using the followingequation.T _(det) =T ₃ −T _(offset)  (3)

Therefore, the second ambient temperature determination algorithm may beconfigured to leverage the slower response of the third temperaturesensor to component-related heating effects. The first ambienttemperature determination algorithm may be ideal during operation in thelow-power mode because it can respond quickly to temperature changes inthe enclosure (e.g. someone leaves a door open in the winter); however,this ability to rapidly respond may be a detriment during operation inthe high-power mode. Instead, in the embodiment described above, anarithmetic offset temperature may be subtracted from the temperaturesensor measurements provided by the third temperature sensor. In otherembodiments, scaling factors may be used, percentages may be calculated,and other combinations of sensors may also be used. In one embodiment, adifference between the second temperature sensor and the thirdtemperature sensor may be used by the second ambient temperaturedetermination algorithm. In another embodiment, measurements from allthree sensors may be used to calculate the determined ambienttemperature. Additional equations and combinations of temperaturesensors may be derived using the principles of this disclosure to meetthe needs of many different enclosures and thermostat types. Theequations described above are merely exemplary, and not meant to belimiting.

While some embodiments may simply switch between the first and secondambient temperature determination algorithms when the thermostatswitches between the low-power mode and the high-power mode, otherembodiments may use additional sensors and algorithms to further refinethe time when this switching should take place in order to minimizefalse negatives and false positives that may be caused by only temporarydirect sunlight exposure and other artificial light sources.

In some embodiments, the transition between the determined ambienttemperature calculated by the first temperature determination algorithmand the determined ambient temperature calculated by the secondtemperature determination algorithm might not be completely continuous.In other words, there may be an abrupt transition between calculatedambient temperatures. Therefore, it may be desirable in some embodimentsto minimize false positives and false negatives by allowing thethermostat components to operate in the high-power mode for a certainperiod of time before switching between algorithms. For example, if auser activates the user interface for only a few seconds, the heatgenerated by the user interface and any processors that power the userinterface might not generate an excessive amount of heat that wouldjustify switching between ambient temperature determination algorithms.

In some embodiments, the thermostat may detect when excessive internalheat is being generated by analyzing the raw temperature measurements ofthe second temperature sensor. For example, a rapid increase intemperature over a short period of time may indicate that thermostatcomponents are generating excessive heat that may distort the determinedambient temperature calculations. However, relying on the secondtemperature sensor measurements to determine when the second temperaturesensor measurements are becoming unreliable may be problematic in theoryand in practice. Instead, some embodiments may use detecting operationin the high-power mode for a certain period of time as a proxy fordetecting excess heat. Some embodiments may combine aspects of these twomethods and made both detect when components are operating in thehigh-power mode and when excessive heat is being generated based ondivergence of a measured or calculated temperature in comparison to anexpected value.

FIG. 9 illustrates a graph 900 of actual temperature measurements as thethermostat switches between the first and second ambient temperaturedetermining algorithms, according to some embodiments. At time t₁, oneor more of the components of the thermostat may begin operating in ahigh-power state. For example, a user interface may be activated inresponse to a user manipulation of a thermostat input control. In othercases, a main processor may wake up to perform temperature calculations.In other cases, power stealing circuitry may enter into a power stealingmode that generates excessive internal heat. In other cases, an HVACfunction may be actuated such that internal power transistors maygenerate excessive heat. In some cases, a combination of any of thesecircumstances may also be detected.

Although the thermostat may detect one or more components beginning tooperate in a high-power mode at time t₁, the thermostat need not switchfrom the first ambient temperature determination algorithm to the secondambient temperature determination algorithm at time t₁. Instead, thethermostat may wait for a first time interval to make sure that the oneor more components operate in the high-power mode for a sufficientamount of time to generate excessive internal heat. For example, thefirst time interval may be represented as the difference between time t₁and time t₂. Accordingly, at time t₂, the thermostat may switch to usethe second ambient temperature determination algorithm.

In FIG. 9, the first temperature sensor curve 910, the secondtemperature sensor curve 912, and the third temperature sensor curve 914may all begin to increase as the thermostat begins to be heated bycomponents operating in the high-power mode. Note that as describedabove, the curve corresponding to each temperature sensor changes atdifferent rates and times based on their location and thermal isolationwithin the thermostat housing relative to the heat-generatingcomponents.

As the first temperature sensor curve 910 and the second temperaturesensor curve 912 begin to increase and diverge, the determined ambienttemperature curve 916 begins to decrease according to the first ambienttemperature determination algorithm. At this point, the thermostat mayswitch to the second ambient temperature determining algorithm. Theresults of this switch may be seen by determined ambient temperaturecurve 918.

Instead of simply relying on detecting components operating in thehigh-power mode, some embodiments may first detect components operatingin the high-power mode, then detect a temperature divergence. Forexample, at time t₁, the thermostat may detect components operating inthe high-power mode. At some point between time t₁ and time t₂, thethermostat may determine that the components have operated in thehigh-power mode for a sufficient time interval to begin watching fortemperature divergence. As the second temperature sensor curve 912begins to diverge from either the third temperature sensor curve 916,the first temperature sensor curve 910, and/or the determined ambienttemperature curve 916, a temperature divergence may be detected. As usedherein, a temperature divergence may refer to an instance where thecurrent difference between the second temperature sensor and the thirdtemperature sensor exceeds the historical difference by some margin(e.g., 0.3° C.). Alternatively, the determined ambient temperature curve916 may be compared to any of the other temperature curves to detect atemperature divergence. At time t₂, the thermostat may determine that(i) one or more components are operating the high-power mode for asufficient period of time, and (ii) that a temperature divergence hasbeen detected, and consequently switch to the second ambient temperaturedetermination algorithm. Determined ambient temperature curve 918represents the determined ambient temperature calculated by the secondambient temperature determination algorithm.

In some cases, the transition between determined ambient temperaturecurve 916 and determined ambient temperature curve 1118 may be abruptand/or discontinuous. This abrupt change may cause unintendedconsequences in the control of the HVAC system. In order to smooth thistransition, some embodiments may use low pass filtering techniques. Oneembodiment may use an averaging sliding window that averages the lastfive to ten temperature measurements at, for example, 30 secondintervals. Other window length and interval lengths may also be used. Inother embodiments, discrete time domain operations may apply digitalfilters to the determined ambient temperatures to smooth the transition.

In order to switch back to the first ambient temperature determinationalgorithm, the thermostat may detect when the one or more componentstransition out of the high-power operating mode back into the low-poweroperating mode. Some embodiments may immediately switch between ambienttemperature determination algorithms. Other embodiments may again wait acertain interval of time before switching algorithms after a transitionbetween operating modes has been detected. For example, at time t₃ thethermostat may detect that the one or more components of transition backinto the low-power operating mode. After a certain time interval haspassed, the thermostat may switch back to the first ambient temperaturedetermination algorithm, such as at time t₄. Some embodiments may alsolook for a temperature convergence that is substantially the opposite ofthe temperature divergence detected earlier. For example, a temperatureconvergence may indicate that the current difference between the secondtemperature sensor and the third temperature sensor is within thehistorical difference by some margin (e.g. 0.15° C.). In someembodiments, there may be a difference between the margins used fordivergence (e.g. 0.3° C.) and convergence (0.15° C.) as a form ofhysteresis to avoid frequently triggering convergence/divergence. Someembodiments may watch for both temperature convergence and the one ormore components operating in the low-power state for more than a certaintime interval, and switch back to the first ambient temperaturedetermination algorithm when either condition is met.

FIG. 10 illustrates a flowchart 1000 of an algorithm that may be used toswitch between ambient temperature determination algorithms, accordingto some embodiments. Flowchart 1000 may be implemented in softwareand/or hardware by a state machine. This algorithm may use bothdetecting component operating modes and temperaturedivergence/convergence to switch between ambient temperaturedetermination algorithms.

In embodiments where the thermostat is divided into a head unit and abackplate, the temperature switching algorithm can be run by the headunit processor. The head unit processor can then store transitiontemperatures and/or operating mode indications in the backplateprocessor. Sometimes, the head unit processor may step through differentstages of the state machine represented by flowchart 1200 each time thehead unit processor wakes up. In some cases, multiple stages may bestepped through in each wake cycle, while in other cases, the statemachine may remain idle.

During normal operation, the thermostat may reside in the idle state1002 while the internal components of the thermostat operate in thelow-power mode. While in the idle state 1002, the thermostat may detecttime intervals wherein one or more components operates in the high-powerstate. After one or more components operates in the high-power state formore than “X” seconds, the thermostat may transition into state 1004 tobegin looking for temperature divergence.

While in state 1004, the thermostat may monitor the one or morecomponents to detect transitions to the low-power state for more than“Y” seconds. In some embodiments, transitioning into state 1004 may onlyrequire one or more of a plurality of internal components operating inthe high-power state for more than “X” seconds. In contrast,transitioning out of state 1004 back to the idle state 1002 may requireall of the internal components to operate in the low-power state formore than “Y” seconds.

While in state 1004, if a temperature divergence is detected, then thethermostat may transition into state 1006 and begin using the secondambient temperature determination algorithm to calculate the determinedambient temperature. In one embodiment, a temperature divergence may bedefined as the instantaneous difference between the second temperaturesensor and the third temperature sensor being greater by a thresholdamount than the historical difference between the second temperaturesensor and the third temperature sensor. In one embodiment, thethreshold amount may be approximately 0.3° C.

While in state 1006, the thermostat may monitor two differentconditions. First, the thermostat may watch the one or more componentsto determine when they have all been asleep or operating in a low-powermode for more than “Z” seconds. When this condition is met, thethermostat may transition back into the idle state 1002. In other words,the internal components may switch back to the low-power operating modewithout necessarily seeing a temperature convergence. This may occurwhen the ambient enclosure temperature decreases enough that acorresponding increase in the determined ambient temperature may not beobserved.

While in state 1006, the thermostat may monitor a second condition,namely temperature convergence. In some embodiments, temperatureconvergence may be defined as the instantaneous difference between thesecond temperature sensor and the third temperature sensor being smallerby a threshold amount than the historical difference between the secondtemperature sensor and the third temperature sensor. In one embodiment,the threshold amount may be approximately 0.15° C.

The times used for each transition in flowchart 1000 (i.e. “X”, “Y”, and“Z”) may be determined experimentally for each type of thermostat and/oreach type of enclosure. In some embodiments, “X” may correspond toapproximately 20 seconds, “Y” may correspond to approximately 900seconds, and/or “Z” may correspond to approximately 7200 seconds.

The states and steps illustrated by flowchart 1000 are merely exemplary,and not meant to be limiting. Other embodiments may add additionalstates and additional criteria for transitioning between states. Oneexample where additional states may be added to flowchart 1000 involvesheating caused by direct sunlight. Time intervals may be detected usingan ambient light sensor (ALS) where the thermostat is exposed to directsunlight for an extended time. The direct sunlight may cause the varioustemperature sensors to heat up non-uniformly and thereby further distortthe temperature calculations. Generally, the direct sunlight heatingproblem may be solved in the same way that the heating problem due toexcessive internal heat generation may be solved. When direct sunlightheating is detected, the thermostat may switch to the second temperaturedetermination algorithm, as the third temperature sensor is lesssusceptible to direct sunlight heating effects. While the ambienttemperature determination algorithms may be similar, detecting a directsunlight heating event may be different from detecting heating due tointernal components operating a high-power mode. A complete explanationof how to detect and compensate for direct sunlight heating may be foundin the commonly-assigned U.S. patent application Ser. No. 13/835,321entitled “HVAC Controller Configurations That Compensate for HeatingCaused by Direct Sunlight” filed on Mar. 15, 2013 and herebyincorporated by reference for all purposes.

In embodiments that compensate for both direct sunlight exposure andinternal heating by components operating in the high-power mode, thesame state machine infrastructure may be used for each operation. Thismay simplify calculations and may require only a single set of wake-upconditions for a high-power processor. More importantly, the signaturesof direct sunlight heating and heating caused by internal components mayoppose each other. With direct sunlight, the first temperature sensormay heat first followed by the second temperature sensor causing anincrease in the determined ambient temperature. With self-heating, thesecond temperature sensor heats first followed by the first temperaturesensor causing a decrease in the determined ambient temperature. Thus insome embodiments divergence may be used to detect sunlight heating,whereas convergence can be used to detect self-heating.

In combining the state machine compensating for direct sunlight heatingwith the state machine compensating for internal heating, a heightenedstate of awareness may be entered by detecting either an ALS spike orcomponents operating in the high-power mode. After entering theheightened state of awareness, the state machine may then look fortemperature divergence/convergence in order to switch to the secondambient temperature determination algorithm. In some embodiments, theremay be a relative priority between the various conditions that may causetemperature anomalies. For example, the sunlight correction portion ofthe state machine may have a higher priority than the self-heatingtemperature correction portion of the state machine. Therefore, in thecase of an ALS Spike, the state machine may transition based on thesunlight correction mode without regard for the high/low poweroperational mode of the thermostat internal components. In the absenceof an ALS Spike, the state machine may instead operate according to thetemperature correction state machine.

Whereas many alterations and modifications of the present invention willno doubt become apparent to a person of ordinary skill in the art afterhaving read the foregoing description, it is to be understood that theparticular embodiments shown and described by way of illustration are inno way intended to be considered limiting. Therefore, reference to thedetails of the preferred embodiments is not intended to limit theirscope.

What is claimed is:
 1. A smart-home device for monitoring or controlling a condition or system in a home, the smart-home device comprising: a housing; a plurality of temperature sensors, each being positioned at different locations, and each being configured to provide temperature sensor measurements; and a processing system disposed within the housing, the processing system being configured to be in operative communication with the one or more temperature sensors to receive the temperature sensor measurements, wherein said processing system is configured to: (i) operate in a plurality of operating states including a first operating state characterized by relatively low power consumption and a corresponding relatively low associated heat generation and a second operating state characterized by relatively high power consumption and a corresponding relatively high associated heat generation; (ii) during time intervals in which the processing system is operating in the first operating state, process the temperature sensor measurements according to a first ambient temperature determination algorithm that uses a first combination of the plurality of temperature sensors; and (iii) during time intervals in which the processing system is operating in the second operating state, process the temperature sensor measurements according to a second ambient temperature determination algorithm that uses a second combination of the plurality of temperature sensors that is different from the first combination of the plurality of temperature sensors.
 2. The smart-home device of claim 1, wherein the plurality of temperature sensors comprises a first temperature sensor, a second temperature sensor, and a third temperature sensor.
 3. The smart-home device of claim 2, wherein the first ambient temperature determination algorithm is based on readings from said first and second temperature sensors to compute the determined ambient temperature.
 4. The smart-home device of claim 2, wherein the second ambient temperature determination algorithm is based on readings from said first and third temperature sensors to compute the determined ambient temperature.
 5. The smart-home device of claim 2, wherein the third temperature sensor is disposed on a portion of the smart-home device such that the third temperature sensor is less susceptible to heating by the processing system than the first temperature sensor.
 6. The smart-home device of claim 2, wherein the second ambient temperature determination algorithm calculates the determined ambient temperature using (i) temperature measurements provided by the third temperature sensor, and (ii) an offset calculated during the time intervals in which the processing system is operating in the first operating state.
 7. The smart-home device of claim 2, wherein the second temperature sensor is disposed on a portion of the smart-home device such that the second temperature sensor is more susceptible to heating by the processing system than the first temperature sensor and the third temperature sensor.
 8. The smart-home device of claim 1, wherein during the time intervals in which the processing system is operating in the second operating state, the processing system is further configured to: (i) detect a change in the determined ambient temperature; and (ii) switch from the first ambient temperature determination algorithm to the second ambient temperature determination algorithm after detecting said change in the determined ambient temperature.
 9. The smart-home device of claim 1, wherein the smart-home device comprises a thermostat monitoring an ambient temperature and controlling a heating, ventilation, and air conditioning system.
 10. A method of compensating for internal heating in a smart-home device, the method comprising: determining, using a processing system of the smart-home device, a current operating state of the processing system, wherein the smart-home device comprises: a housing; a plurality of temperature sensors, each being positioned at different locations, and each being configured to provide temperature sensor measurements; and a processing system disposed within the housing, the processing system being configured to be in operative communication with the one or more temperature sensors to receive the temperature sensor measurements, wherein said processing system is configured to operate in a plurality of operating states including a first operating state characterized by relatively low power consumption and a corresponding relatively low associated heat generation and a second operating state characterized by relatively high power consumption and a corresponding relatively high associated heat generation; during time intervals in which the processing system is operating in the first operating state, processing the temperature sensor measurements according to a first ambient temperature determination algorithm that uses a first combination of the plurality of temperature sensors; and during time intervals in which the processing system is operating in the second operating state, processing the temperature sensor measurements according to a second ambient temperature determination algorithm that uses a second combination of the plurality of temperature sensors that is different from the first combination of the plurality of temperature sensors.
 11. The method of claim 10, wherein the plurality of temperature sensors comprises a first temperature sensor, a second temperature sensor, and a third temperature sensor.
 12. The method of claim 11, wherein the first ambient temperature determination algorithm is based on readings from said first and second temperature sensors to compute the determined ambient temperature.
 13. The method of claim 11, wherein the second ambient temperature determination algorithm is based on readings from said first and third temperature sensors to compute the determined ambient temperature.
 14. The method of claim 11, wherein the third temperature sensor is disposed on a portion of the smart-home device such that the third temperature sensor is less susceptible to heating by the processing system than the first temperature sensor.
 15. The method of claim 11, wherein the second ambient temperature determination algorithm calculates the determined ambient temperature using (i) temperature measurements provided by the third temperature sensor, and (ii) an offset calculated during the time intervals in which the processing system is operating in the first operating state.
 16. The method of claim 11, wherein the smart-home device comprises a first modular section and a second modular section, the third temperature sensor being disposed in the first modular section, the first temperature sensor being disposed in the second modular section, and the second temperature sensor being disposed in the second modular section.
 17. The method of claim 11, wherein the second temperature sensor is disposed on a portion of the smart-home device such that the second temperature sensor is more susceptible to heating by the processing system than the first temperature sensor and the third temperature sensor.
 18. The method of claim 10, wherein during the time intervals in which the processing system is operating in the second operating state, the processing system is further configured to: (i) detect a change in the determined ambient temperature; and (ii) switch from the first ambient temperature determination algorithm to the second ambient temperature determination algorithm after detecting said change in the determined ambient temperature.
 19. The method of claim 18, wherein the processing system is further configured to switch from the first ambient temperature determination algorithm to the second ambient temperature determination algorithm after determining that the processing system has been operating the second operating state for a predetermined time interval.
 20. The method of claim 10, wherein the smart-home device comprises a thermostat monitoring an ambient temperature and controlling a heating, ventilation, and air conditioning system. 